1=pod 2 3=head1 NAME 4 5SSL_set1_host, SSL_add1_host, SSL_set_hostflags, SSL_get0_peername - 6SSL server verification parameters 7 8=head1 SYNOPSIS 9 10 #include <openssl/ssl.h> 11 12 int SSL_set1_host(SSL *s, const char *host); 13 int SSL_add1_host(SSL *s, const char *host); 14 void SSL_set_hostflags(SSL *s, unsigned int flags); 15 const char *SSL_get0_peername(SSL *s); 16 17=head1 DESCRIPTION 18 19These functions configure server hostname checks in the SSL client. 20 21SSL_set1_host() sets in the verification parameters of I<s> 22the expected DNS hostname or IP address to I<host>, 23clearing any previously specified IP address and hostnames. 24If I<host> is NULL or the empty string, IP address 25and hostname checks are not performed on the peer certificate. 26When a nonempty I<host> is specified, certificate verification automatically 27checks the peer hostname via L<X509_check_host(3)> with I<flags> as specified 28via SSL_set_hostflags(). Clients that enable DANE TLSA authentication 29via L<SSL_dane_enable(3)> should leave it to that function to set 30the primary reference identifier of the peer, and should not call 31SSL_set1_host(). 32 33SSL_add1_host() adds I<host> as an additional reference identifier 34that can match the peer's certificate. Any previous hostnames 35set via SSL_set1_host() or SSL_add1_host() are retained. 36Adding an IP address is allowed only if no IP address has been set before. 37No change is made if I<host> is NULL or empty. 38When an IP address and/or multiple hostnames are configured, 39the peer is considered verified when any of these matches. 40This function is required for DANE TLSA in the presence of service name indirection 41via CNAME, MX or SRV records as specified in RFCs 7671, 7672, and 7673. 42 43TLS clients are recommended to use SSL_set1_host() or SSL_add1_host() 44for server hostname or IP address validation, 45as well as L<SSL_set_tlsext_host_name(3)> for Server Name Indication (SNI), 46which may be crucial also for correct routing of the connection request. 47 48SSL_set_hostflags() sets the I<flags> that will be passed to 49L<X509_check_host(3)> when name checks are applicable, by default 50the I<flags> value is 0. See L<X509_check_host(3)> for the list 51of available flags and their meaning. 52 53SSL_get0_peername() returns the DNS hostname or subject CommonName 54from the peer certificate that matched one of the reference 55identifiers. When wildcard matching is not disabled, the name 56matched in the peer certificate may be a wildcard name. When one 57of the reference identifiers configured via SSL_set1_host() or 58SSL_add1_host() starts with ".", which indicates a parent domain prefix 59rather than a fixed name, the matched peer name may be a sub-domain 60of the reference identifier. The returned string is allocated by 61the library and is no longer valid once the associated I<ssl> handle 62is cleared or freed, or a renegotiation takes place. Applications 63must not free the return value. 64 65SSL clients are advised to use these functions in preference to 66explicitly calling L<X509_check_host(3)>. Hostname checks may be out 67of scope with the RFC 7671 DANE-EE(3) certificate usage, and the 68internal check will be suppressed as appropriate when DANE is 69enabled. 70 71=head1 RETURN VALUES 72 73SSL_set1_host() and SSL_add1_host() return 1 for success and 0 for 74failure. 75 76SSL_set_hostflags() returns nothing at all. 77 78SSL_get0_peername() returns NULL if peername verification is not 79applicable (as with RFC 7671 DANE-EE(3)), or no trusted peername was 80matched. Otherwise, it returns the matched peername. To determine 81whether verification succeeded call L<SSL_get_verify_result(3)>. 82 83=head1 EXAMPLES 84 85Suppose "smtp.example.com" is the MX host of the domain "example.com". 86The calls below will arrange to match either the MX hostname or the 87destination domain name in the SMTP server certificate. Wildcards 88are supported, but must match the entire label. The actual name 89matched in the certificate (which might be a wildcard) is retrieved, 90and must be copied by the application if it is to be retained beyond 91the lifetime of the SSL connection. 92 93 SSL_set_hostflags(ssl, X509_CHECK_FLAG_NO_PARTIAL_WILDCARDS); 94 if (!SSL_set1_host(ssl, "smtp.example.com")) 95 /* error */ 96 if (!SSL_add1_host(ssl, "example.com")) 97 /* error */ 98 99 /* XXX: Perform SSL_connect() handshake and handle errors here */ 100 101 if (SSL_get_verify_result(ssl) == X509_V_OK) { 102 const char *peername = SSL_get0_peername(ssl); 103 104 if (peername != NULL) 105 /* Name checks were in scope and matched the peername */ 106 } 107 108=head1 SEE ALSO 109 110L<ssl(7)>, 111L<X509_check_host(3)>, L<SSL_set_tlsext_host_name(3)>, 112L<SSL_get_verify_result(3)>, L<SSL_dane_enable(3)> 113 114=head1 HISTORY 115 116These functions were added in OpenSSL 1.1.0. 117 118=head1 COPYRIGHT 119 120Copyright 2016-2025 The OpenSSL Project Authors. All Rights Reserved. 121 122Licensed under the Apache License 2.0 (the "License"). You may not use 123this file except in compliance with the License. You can obtain a copy 124in the file LICENSE in the source distribution or at 125L<https://www.openssl.org/source/license.html>. 126 127=cut 128